Duck! Asteroid 2012 TC4 To Fly By Earth Tonight

Asteroid 2012 TC4 looks like a star in this recent photo. The stars show as trails because the telescope tracked the moving asteroid during the time exposure. Credit: Ernesto Guido, Giovanni Sostero & Nick Howes

An asteroid the size of my front yard will zoom by 59,650 miles from, well, my front yard tonight. At average walking speed, you could step from one end of this boulder to the other in just 13 seconds.

2012 TC4 was discovered on October 4 with the 1.8-meter telescope at Haleakala Observatory in Hawaii as part of the Pan-STARRS survey to discover and characterize Earth-approaching comets and asteroids that might become a hazard to the planet.

Asteroid 2012 TC’s orbit will bring it just under 60,000 miles (96,000 km) from Earth late tonight. Credit: JPL

No one’s in danger from this midget asteroid because it’s much too far away to trouble the lumbering Earth. If anything, our planet’s gravity will likely bend and alter 2012 TC4’s path during closest approach. That happens at 12:31 a.m. (CDT) tomorrow morning Oct. 12.

Amateur and professional astronomers have been studying the asteroid’s light variations since discovery and determined that it rotates very quickly, perhaps as fast as one spin every 12 minutes. Its brightness also varies by about 1 magnitude during a rotation. These are good things to keep in mind if you’re considering tracking it tonight.

You’ll need at least a 10-inch telescope and haze-free skies to find this hasty rock. Not only will it be moving quickly in front of the stars but at brightest will shine only between 13.6-14.0 magnitude. That’s over 1500 times fainter than the faintest star most of us can see with the unaided eye. Around the time of closest approach, 2012 TC4 will be peeling through the stars of Sagittarius at approximately one degree (two full moon diameters) every 5 minutes. If you can catch up with our little friend, you’ll see it cross the telescopic field of view in real time just like a man-made satellite.

The approximate track of the asteroid through the constellations Capricornus and Sagittarius. Times are CDT. For mid-northern latitudes, 2012 TC4 will be low in the southern sky and set before midnight. Created with Chris Marriott’s SkyMap software.

Tracking something that fast and faint requires making your own maps using star charting, planetarium-style programs like SkyMapMegaStar, Cartes du Ciel (free) or a scope with automatic pointing ability. These programs have the option of adding an asteroid and its orbital elements to the database. With that information, you can print your own chart showing its path. Click HERE for 2012 TC4’s orbital elements for manual input or HERE to download them right into your program.

If that fails, you can hand-plot its position on a star atlas. Since 2012 TC4 will be so close to Earth, different locations will see the asteroid take slightly different paths across the sky,  this might be the best option. To find the path for your location, you’ll need to go to JPL’s HORIZONS Web-Interface site, change the observer location line, select your time span and then click the Generate ephemeris button for a table of positions of the asteroid for every minute, every hour, etc. Remember that the times shown in the table are Universal Time (UT). Subtract 4 hours for Eastern Daylight, 5 for Central, 6 for Mountain and 7 Pacific.

Venus and the thin crescent moon – a great way to start the day tomorrow. This view shows the sky facing east at 6:30 a.m. local time Friday. Created with Stellarium

If all this asteroid talk is bit much, how about something brighter and easier to see? Luckily, we have just the thing tomorrow morning October 12 at dawn, when the crescent moon will shine near the planet Venus. Nice to know there’s something for everybody out there.

23 Responses

  1. Dennis Lammens

    Astro Bob – have you written any basic books of Astronomy, if so where can I get one or two. We live in Arizona, so a trip to the Columbia Mall bookstore is out of the question.

  2. lynn

    I agree Bob you should definitely get someone to publish your book and we can all back you up on how good you are :-).
    Is all your family interested in astronomy Bob?

    1. astrobob

      I appreciate both your votes of confidence. Thanks! My daughters have an interest (my older daughter appreciates seeing the stars when visiting from the city; the younger one casually follows astro events), my wife a little and my younger brother, too. And your family?

  3. lynn

    Well at least you will be able to keep everyone with your great knowledge Bob. My eldest daughter hasn’t really got an interest in it but a few times she has aaked me what certain things have been in the night sky so I have been able to tell her through reading your blog, my second eldest just enjoys travelling around but my youngest is quite intetested and has asked me to buy her a telescope but I wouldn’t know where to start so if you can recommend a good one for her for just starting off that would be good. Thanks Bob 🙂

    1. astrobob

      How old is your youngest and how much do you have to spend? I can give a recommendation if you’d like.

  4. lynn

    She is 15 and I wouldn’t like to spend a huge amount just a basic start off one just to make sure she really is keen and then if I know she is really interested then I would look at something a bit more expensive, as you will know Bob teenagers go through phases and I wouldn’t like to pay for one thats really expensive and the novelty wears off and it gets left gathering dust 🙂

  5. MBZ

    I would recommend a pair of decent binoculars and whatever book Bob thinks best for your daughter. Going directly to a telescope can be off-putting, especially at her age.
    And I too would enjoy a book Mr. A.B., but only if you promise to sign it.

  6. Dee White

    What kind of binocular…meaning strength? I have a telescope that has sat in 3 different rooms of our house, now it is residing in the garage. Sadly, I’m a dinosaur technically and can not figure out how to operate it. Binoculars I think I can manage. *!*
    I have always enjoyed the night sky. We moved to a home where I can really see the stars at night a few years ago. I find the night sky so calming and also fascinating. I heard and have read that all of time can be read in the night sky (although don’t ask me to explain it, I was barely able to understand how “they” do that)…amazing!

    1. astrobob

      Hi Dee,
      A good balance of magnification and brightness is a pair of 8×40 or 10×50 binoculars. The first number is the magnification, the second is the diameter of the lens in millimeters that gathers the light. You can get a very inexpensive, excellent pair of 8×40 Nikons ( or 10x50s Nikons ( Other brands like Pentax are good, too. I own 8×40 Nikons and they’re a real deal for the quality. My other favorite pair are wide-angle Pentax 10x50s. Those give the best views of the Milky Way from a dark sky.

  7. Ken W.

    I took a picture of Venus and the crescent moon this morning…..then I went to see the space shuttle in L.A.

    1. astrobob

      Hi Ken,
      Sounds like a great day. I missed Venus and the moon but saw photos of the space shuttle on the streets of LA. It looked so odd between power poles and grocery stores.


    Hello Astro Bob,
    I was wondering if you could help me confirm something, some years ago I was out in the Cal. desert around sunset when i saw a large blue oblong object shoot across the sky. It was traveling somewhat low and had a medium length white tail. No sound and was traveling quite fast. Could this have been a “skimmer” meteor I saw. ( please no jokes about Californians) Thank you.Mark

    1. astrobob

      Hi Mark,
      It was probably a fireball seen from a great distance. Generally, the lower the meteor is in the sky, the farther away it is from the observer. It’s hard to say from your observation if it skipped back into space. Most burn up and don’t return. How long was it visible?

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